Orbiter solves Martian mysteries

Emma Woollacott, 27th May 2010

NASA's Mars Reconnaissance Orbiter (MRO) has helped solve two forty-year-old mysteries and delivered new information about climate change on Mars.

Its Shallow Radar, or Sharad, instrument has revealed the subsurface geology, allowing scientists to reconstruct the formation of a large chasm and a series of spiral troughs on the planet's northern ice cap.

On Earth, large ice sheets are shaped mainly by ice flow. But the new data indicates that other forces are at work on the polar ice caps on Mars.

One distinctive feature is Chasma Boreale, a canyon about as long as Earth's Grand Canyon but deeper and wider. Some scientists believe it was created when volcanic heat melted the bottom of the ice sheet and triggered a massive flood. Others suggest strong polar winds carved the canyon out of a dome of ice.

One weird aspect of the ice cap is a series of troughs, discovered in 1972, that spiral outward from the center. Scientists have proposed several hypotheses about how they formed.

One suggestion was that as Mars spins, ice closer to the poles moves slower than ice farther away, causing it to crack. One mathematical model suggested that increased solar heating in certain areas and lateral heat conduction could generate the troughs.

But the new data points to both the canyon and the troughs being created and shaped primarily by wind over millions of years as the ice sheet grew. By influencing wind patterns, the shape of underlying, older ice controlled where and how they appeared.

"Nobody realized that there would be such complex structures in the layers," said lead author Jack Holt of the University of Texas.

"The layers record a history of ice accumulation, erosion and wind transport. From that, we can recover a history of climate that's much more detailed than anybody expected."

"These anomalous features have gone unexplained for 40 years because we have not been able to see what lies beneath the surface," said Roberto Seu, Sharad team leader at the University of Rome. "It is gratifying to me that with this new instrument we can finally explain them."